The invention relates to a two-roll casting installation with two casting rolls which rotate in opposite directions about horizontal axes, with a casting gap for forming and discharging a thin cast metal strip, with a sealed housing which has a base and surrounds the conveying path for the metal strip which leaves the casting gap from a vertical casting direction into an approximately horizontal conveying direction, with diverter devices for diverting the metal strip within this housing, and with a displaceable scrap collection container for removing scrap and scale produced from the two-roll casting installation. The invention also relates to a method for initiating a casting process using the two-roll casting device according to the invention.
Two-roll casting installations are used to produce metal strips, preferably steel strips, with a large strip width and with a strip thickness of less than 10 mm in a continuous casting process. In particular in the case of carbon steels, there is a high likelihood of scaling on contact with oxygen at high temperatures, and consequently the metal melt and the cast metal strip, until the latter has substantially cooled, are passed through a protective gas atmosphere which does not have an oxidizing action.
WO 02/11924 has already disclosed a two-roll casting installation of the generic type. It comprises two casting rolls which rotate in opposite directions about horizontal axes of rotation and, together with side plates which can be placed onto the end sides of the casting rolls, form a melt space and a casting gap, out of which a cast metal strip is discharged vertically downward. The cast metal strip is diverted into the horizontal, so as to form a hanging loop, and then fed to one or more further treatment devices. As it emerges from the casting gap, the hot metal strip passes through a sealed chamber with a protective gas atmosphere, which substantially prevents oxidation processes at the surface of the metal strip. All the openings in this chamber are provided with sealed gates or locks.
The sealed chamber also comprises a space which is open toward the casting rolls for receiving a movable scrap carriage, which, via a lock system which can be flooded with protective gas, can be moved into a receiving position beneath the two casting rolls for the scrap and scale produced and can be removed from this position. To manipulate the scrap carriage, large lock gates have to be opened and large spaces accommodating the scrap carriage have to be flooded with protective gas. Furthermore, complex sealing systems have to be installed for the large lock gates.
Furthermore, WO 02/11924 has disclosed a pivotable guide flap for the cast metal strip, which in an operating position assists with diverting the metal strip into the horizontal and toward a pinch-roll stand and, in a retracted position, allows vertical discharging of a piece of the strand into the scrap bucket. A solution of this type is also known from WO 01/23120.
EP-B 726 112 and WO 01/39914 have disclosed two-roll casting installations of the generic type, in which the cast metal strip is passed through an insulated chamber without integrated base region. The base region is formed by a scrap bucket which can be pressed vertically onto the end sides of the side walls of the insulated chamber and rests on a displaceable scrap carriage such that it can be raised and lowered. A seal is provided between the side walls of the insulated chamber and the edges of the scrap bucket, by means of which seal the insulated chamber is closed off in a substantially gastight manner. When changing the scrap bucket once it has been filled with scrap, the protective gas atmosphere in the insulated chamber through which the metal strip passes is also lost, and it is necessary for the entire chamber to be flooded with protective gas after an empty scrap bucket has been reintroduced; during this operation, it is inevitable that a relatively large quantity of external air and therefore residual oxygen will remain behind. This increases the formation of scale on the metal strip which is subsequently cast for a relatively long period of time, and therefore leads to increased scrap or to adverse consequences for the surface quality of the cast strip. Consequently, the scrap bucket can only be emptied during breaks in production.